JP2007327460A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of attaining PM purification efficiency of a high level, by sufficiently restraining reduction in an oxidation speed of PM by NOx, by efficiently using ozone, when oxidizing and removing the PM by using the ozone, in a device for purifying exhaust gas exhausted from an internal combustion engine such as a diesel engine, by using a particulate matter collecting device for collecting the PM in the exhaust gas. <P>SOLUTION: This exhaust emission control device is characterized by having an exhaust gas passage 15 connected to the internal combustion engine 10, the particulate matter collecting device 30 arranged in the exhaust gas passage 15 and collecting particulate matter in the exhaust gas, an ozone supply means 40 connected to the exhaust gas passage 15 on the upstream side of the particulate matter collecting device 30 and capable of supplying the ozone to the particulate matter collecting device 30, and an NO oxidizing catalyst 20 arranged in the exhaust gas passage 15 on the upstream side of the ozone supply means 40 and oxidizing NO in the exhaust gas. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus, and more particularly to an apparatus for purifying exhaust gas discharged from an internal combustion engine such as a diesel engine using a particulate matter collection device that collects particulate matter in the exhaust gas.

In general, exhaust gas from a diesel engine contains particulate matter (hereinafter referred to as “PM (Particulate Matter)”) containing carbon as a main component, and is known to cause air pollution. Therefore, various apparatuses and methods for capturing and removing these particulate substances from exhaust gas have been proposed. For example, (i) a diesel particulate filter (hereinafter, “ (Ii) a method in which the collected PM is oxidized and burned by raising the temperature of the DPF, and (ii) a method in which NO ₂ is produced from NO in the exhaust gas and the PM is oxidized by NO ₂ No. 531762 (Patent Document 1), (iii) a method for oxidizing PM using a catalyzed DPF (for example, JP-A-6-272541 (Patent Document 2), JP-A-9-125931 ( Patent Document 3)) has been proposed.

However, in the method (i), the fuel is forcibly injected and fuel consumption is deteriorated, and PM burns rapidly, and the DPF is damaged due to a rapid temperature change derived from the reaction heat at that time. There was a problem that there was. Further, the method (ii) has a problem that it is difficult to completely oxidize and remove PM discharged from the engine because the oxidation rate of PM by NO ₂ is not sufficient. Furthermore, in the method (iii), since the catalyst and the PM are both solid, there is a problem that the two are not sufficiently in contact with each other and the PM oxidation reaction is insufficient.

Therefore, recently, a technique for oxidizing and treating PM using ozone (O ₃ ) having a stronger oxidizing power than NO ₂ has been disclosed (for example, Japanese Translation of PCT International Publication No. 2005-502823 (Patent Document 4)). ). In the method for post-processing the exhaust gas of a diesel engine described in Patent Document 4, an apparatus for generating ozone or NO ₂ as an oxidant from the exhaust gas by plasma is provided upstream of the particulate filter, depending on the temperature of the exhaust gas. ozone and NO ₂ at low temperatures Te, at high temperatures by using selectively the NO _2, has a PM trapped in the particulate filter so as to remove oxide.

However, in the method described in Patent Document 4, ozone is generated by plasma from oxygen which is a component of exhaust gas, and exhaust gas containing NO _{x and the} like is introduced into the particulate filter together with the generated ozone. Before the strong ozone enters the particulate filter, it reacts with NO _x in the exhaust gas and is consumed, and the amount of ozone used for the oxidation removal of PM decreases and sufficient purification efficiency cannot be obtained. There was a problem that the oxidation rate of PM decreased.
Special Table 2002-53762 JP-A-6-272541 JP-A-9-125931 JP 2005-502823 A

This invention is made | formed in view of the subject which the said prior art has, and purifies the exhaust gas discharged | emitted from internal combustion engines, such as a diesel engine, using the particulate matter collection device which collects PM in exhaust gas. In the equipment, when oxidizing and removing PM using ozone, ozone can be used efficiently, and a high level of PM purification efficiency is achieved by sufficiently suppressing a decrease in the oxidation rate of PM due to NO _x or the like. An object of the present invention is to provide an exhaust gas purifying apparatus capable of performing the above.

The present inventors have made intensive studies to achieve the above object, the ozone has a property of easily reacting with NO _x and HC in exhaust gas, particularly liable to react NO, and ozone supply By arranging the NO oxidation catalyst upstream of the means, the consumption of ozone due to the reaction with NO _x is suppressed, the decrease in the PM oxidation rate is sufficiently suppressed, and a high level of PM purification efficiency is achieved. As a result, the present invention has been completed.

That is, the exhaust gas purification apparatus of the present invention is
An exhaust gas passage connected to the internal combustion engine;
A particulate matter collecting device disposed in the exhaust gas passage for collecting particulate matter in the exhaust gas;
An ozone supply means connected to the exhaust gas passage upstream of the particulate matter collection device and capable of supplying ozone to the particulate matter collection device;
A NO oxidation catalyst which is disposed in the exhaust gas passage upstream of the ozone supply means and oxidizes NO in the exhaust gas;
It is characterized by providing.

According to the exhaust gas purification apparatus of the present invention, since the NO oxidation catalyst is disposed upstream of the ozone supply means, at least a part of NO in the exhaust gas is NO ₂ by the NO oxidation catalyst in advance on the upstream side of the ozone supply means. In particular, the amount of NO that is oxidized and easily reacts with ozone is reduced. Thereby, the consumption of ozone by NO _x in the exhaust gas is suppressed, because more amount of ozone is to be used for the oxidation removal of PM in the particulate matter trapping device, decrease in the oxidation rate of PM is Sufficiently suppressed and a high level of PM purification efficiency is achieved.

  The exhaust gas purifying apparatus of the present invention comprises an exhaust gas temperature detecting means for measuring or estimating a temperature of exhaust gas passing through the particulate matter collecting device, and the ozone supply means based on the exhaust gas temperature detected by the exhaust gas temperature detecting means. It is preferable to further comprise an ozone supply control means for controlling, in which case the ozone supply control means has the exhaust gas temperature not lower than a first predetermined temperature not lower than 50 ° C. and not higher than a second predetermined temperature not higher than 300 ° C. It is particularly preferable to control the ozone supply means so as to supply ozone when the value is within the range.

When the exhaust gas temperature is 50 ° C. or higher, NO tends to be more efficiently oxidized to NO ₂ by the NO oxidation catalyst, and when the exhaust gas temperature is 300 ° C. or lower, the reactivity between NO and ozone is NO ₂ . It tends to be higher than the reactivity with ozone. Therefore, according to the preferred exhaust gas purifying apparatus of the present invention, since the consumption of ozone by NO _{x in} the exhaust gas is more reliably suppressed, the decrease in the PM oxidation rate is more sufficiently suppressed. Therefore, a higher level of PM purification efficiency is achieved.

According to the present invention, in a device for purifying exhaust gas discharged from an internal combustion engine such as a diesel engine using a particulate matter collecting device that collects PM in exhaust gas, when oxidizing and removing PM using ozone In addition, it is possible to provide an exhaust gas purification device that can efficiently use ozone and sufficiently suppress a decrease in the oxidation rate of PM due to NO _x or the like and achieve a high level of PM purification efficiency. Become.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  FIG. 1 shows a schematic diagram of a preferred embodiment of the exhaust gas purification apparatus of the present invention connected to an internal combustion engine. In FIG. 1, 10 is a compression ignition type internal combustion engine (ie, diesel engine), 11 is an intake manifold communicated with an intake port, 12 is an exhaust manifold communicated with an exhaust port, and 13 is a combustion chamber. The fuel supplied from a fuel tank (not shown) to the high pressure pump 17 is pumped to the common rail 18 by the high pressure pump 17 and accumulated in a high pressure state. The high pressure fuel in the common rail 18 is transferred from the fuel injection valve 14 to the combustion chamber 13. Injected directly into the inside. The exhaust gas from the diesel engine 10 passes from the exhaust manifold 12 through the turbocharger 19 and then flows into the exhaust gas passage 15 downstream thereof. After being purified as described in detail below, the exhaust gas is discharged to the atmosphere. In addition, as a form of a diesel engine, it is not restricted to the thing provided with such a common rail type fuel injection device.

  In the exhaust gas passage 15 shown in FIG. 1, in order from the upstream side, a NO oxidation catalyst 20 that oxidizes NO in the exhaust gas, and diesel as a particulate matter collection device that collects particulate matter (PM) in the exhaust gas. A particulate filter (hereinafter referred to as “DPF”) 30 is arranged in series.

As the NO oxidation catalyst 20 according to the present invention, a catalyst that includes a porous oxide carrier and a noble metal supported thereon and can efficiently oxidize NO in exhaust gas to NO ₂ is preferably used. . The metal oxide constituting such a porous oxide carrier is not particularly limited. For example, alumina, silica, titania, zirconia, ceria, ceria-alumina solid solution, ceria-titania solid solution, ceria-zirconia solid solution, zirconia -A titania solid solution, a silica-alumina solid solution, a zeolite, etc. can be mentioned. In addition, the porous oxide carrier can be used as a single oxide of a single metal oxide, a combination of two or more metal oxides, or a composite oxide. The amount of the porous oxide carrier is not particularly limited, but is preferably in the range of 30 to 400 g per liter of the base material described later.

  Examples of the noble metal include platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), and ruthenium (Ru). Among these, Pt is particularly preferable from the viewpoint of high NO oxidation activity. The amount of such noble metal supported is not particularly limited, but is preferably in the range of 0.1 to 20 g per liter of the base material described later.

  Moreover, you may carry | support metals, such as V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, In, on a porous oxide support | carrier.

  The form of the NO oxidation catalyst 20 according to the present invention is not particularly limited, and may be in the form of a honeycomb-shaped monolith catalyst, a pellet-shaped pellet catalyst, or the like. The substrate used here is not particularly limited, and a monolith substrate, a pellet substrate, a plate substrate and the like are preferably employed. Among them, the effect of the present invention is more sure when a monolith substrate is used. Tend to be achieved. Also, the material of such a substrate is not particularly limited, but a substrate made of a ceramic such as cordierite, silicon carbide, mullite, or a substrate made of a metal such as stainless steel including chromium, nickel and aluminum is preferable. Adopted.

  Specific examples of the NO oxidation catalyst 20 according to the present invention include, for example, JP-A-8-103636, JP-A-8-243356, JP-A-9-299795, and JP-A-2001-115824. , JP 2002-35587 A, JP 2002-89246 A, JP 2003-80033 A, JP 2003-205223 A, JP 2004-167354 A, JP 2006-46286 A. NO oxidation catalyst.

The form of the DPF 30 according to the present invention is not particularly limited, and may be a wall flow type as shown in FIG. 1 or a foam type. The wall flow type DPF has a honeycomb structure in which a first passage with a plug on the downstream side and a second passage with a plug on the upstream side are alternately formed. The exhaust gas passes from the first passage through the flow passage wall surface, flows into the second passage and flows downstream, and at that time, PM in the exhaust gas is collected by the flow passage wall surface. The material of the DPF 30 is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, silica, alumina, mullite, or a base material made of a metal such as stainless steel including chromium, nickel, and aluminum is preferable. Adopted. Note that if the DPF 30 is coated with a catalyst such as a noble metal, it tends to be decomposed before O ₃ oxidizes PM. Therefore, it is preferable that the DPF 30 is not coated with a catalyst.

In the exhaust gas purification apparatus of the present invention shown in FIG. 1, ozone (O ₃ ) can be supplied to the DPF 30 between the NO oxidation catalyst 20 and the DPF 30, that is, downstream of the NO oxidation catalyst 20 and upstream of the DPF _30. A simple ozone supply means 40 is connected. The ozone supply means 40 includes an ozone generator 41 as an ozone generation means, and an ozone supply nozzle 43 connected to the ozone generator 41 via an ozone supply passage 42.

As the ozone generator 41 according to the present invention, a form in which ozone is generated while flowing air or oxygen as a raw material in a discharge tube to which a high voltage can be applied, and other arbitrary types can be used. Since NO _x is generated when nitrogen is present in the gas supplied to the ozone generator 41, it is preferable to supply only oxygen.

  Note that air or oxygen as a raw material here is a gas taken from outside the exhaust gas passage, for example, a gas contained in the outside air, unlike the case of Patent Document 4, and is contained in the exhaust gas in the exhaust gas passage as in Patent Document 4. It is not a gas. Further, in the ozone generator 41, the ozone generation efficiency is higher when the low temperature source gas is used than when the high temperature source gas is used. Therefore, by generating ozone using the gas outside the exhaust gas passage in this way, it is possible to improve the ozone generation efficiency as compared with the case of Patent Document 4.

The ozone supply nozzle 43 according to the present invention is arranged at a position immediately upstream of the DPF 30 so that the ozone supplied and supplied from this reacts with NO _x or the like in the exhaust gas and is not easily consumed. Is preferably supplied. Moreover, it is preferable to have a plurality of ozone supply ports 44 that extend over the entire diameter of the upstream end surface of the DPF 30 so that ozone can be uniformly supplied to the entire upstream end surface of the DPF 30. As the form of the ozone supply means 40, various forms other than those having the ozone supply nozzle 43 are possible. For example, when only one ozone supply port is provided, It is preferable that the distance from the upstream end face of the DPF be separated by a distance that allows ozone to spread throughout the entire upstream end face.

  Further, in the exhaust gas purification apparatus of the present invention shown in FIG. 1, a temperature sensor 50 is provided as exhaust gas temperature detection means for measuring the temperature of the exhaust gas passing through the DPF 30, and based on the exhaust gas temperature detected by the temperature sensor 50. The ECU 100 is electrically connected to an ECU 100 serving as an ozone supply control unit that controls the ozone supply unit 40. The exhaust gas temperature detecting means according to the present invention is not limited to the temperature sensor 50, and the temperature of the exhaust gas passing through the DPF 30 is estimated using engine characteristic map data stored in the ECU 100 based on the operating state of the engine and the like. It may be a means to do. In the exhaust gas purification apparatus of the present invention, although not shown, an exhaust pressure sensor that detects the amount of PM trapped and the degree of clogging by the differential pressure on the upstream and downstream sides of the DPF 30, and the air-fuel ratio of the exhaust gas flowing into the DPF 30 are detected. An air-fuel ratio sensor or the like may be provided.

According to the exhaust gas purification apparatus of the present invention shown in FIG. 1 described above, at least a part (preferably all) of NO in the exhaust gas is oxidized to NO ₂ by the NO oxidation catalyst 20 described above. When the ozone from the ozone supply means 40 to the flue gas is supplied, ozone reacts with NO _x and ozone in accordance with the following reaction formula can be consumed.
NO + O ₃ → NO ₂ + O ₂ (1)
NO ₂ + O ₃ → NO ₃ + O ₂ (2)
2NO ₃ → 2NO ₂ + O ₂ (3).

However, since the reactivity between ozone and NOx is lower in NO ₂ than NO, it is consumed in the reaction (1) by previously oxidizing NO in exhaust gas to NO ₂ as described above. Is suppressed, and a larger amount of ozone is subsequently used for the oxidation removal of PM in the DPF 30. Therefore, a decrease in the oxidation rate of PM is sufficiently suppressed, and a high level of PM purification efficiency is achieved. Will be achieved.

Then, in the DPF 30, by reaction with ozone and PM shown below, PM is removed as CO and CO _2.
C + O ₃ → CO + O ₂ (4)
C + 2O ₃ → CO ₂ + 2O ₂ (5).

According to the present inventors, the following knowledge has been obtained. That is, decomposition of O ₃ starts at about 200 ° C. or higher, and PM starts to be oxidized by NO ₂ at 200 ° C. or higher. Furthermore, as shown in FIG. 2, when the input amount of ozone is 500 ppm, the reactivity of ozone with NOx at 300 ° C. or less (preferably 250 ° C. or less) has become lower in NO ₂ than NO When the temperature exceeds 300 ° C., the reactivity between NO ₂ and ozone tends to increase.

Therefore, in the exhaust gas purification apparatus of the present invention, the exhaust gas temperature passing through the DPF 30 is a first predetermined temperature that is 50 ° C. or higher (more preferably 100 ° C. or higher) and 300 ° C. or lower (more preferably 250 ° C. or lower). The ozone is supplied from the ozone supply means 40 when the temperature is within a predetermined temperature range, and in a high temperature region exceeding 300 ° C. (more preferably 250 ° C.), ozone is not supplied and the NO oxidation catalyst is used. It is preferable to oxidize PM only with the produced NO ₂ . By controlling the ozone supply means 40 in this way, the consumption of ozone by NO _{x in} the exhaust gas is more reliably suppressed, so that the reduction in the oxidation rate of PM is more sufficiently suppressed and a higher level is achieved. PM purification efficiency is achieved.

  Note that the ozone supply timing is preferably when the amount of PM collected in the DPF 30 is equal to or greater than a predetermined value.

Further, in order to reliably oxidize NO with NO ₂ by the NO oxidation catalyst 20, a temperature of 50 ° C. or higher is necessary, and a temperature of 100 ° C. or higher is more preferable. As long as it is installed on the upstream side of the exhaust gas passage 15, it is preferable.

Furthermore, in the exhaust gas purifying apparatus of the present invention, it is preferable to reduce the amount of NO _x in the exhaust gas in advance by using another exhaust gas purifying device such as an EGR device in combination. With such advance is previously reduced amount of NO _x in the exhaust gas tends to further improve oxidation efficiency of the PM decreases more the consumption of ozone.

  The preferred embodiment of the exhaust gas purifying apparatus of the present invention has been described above, but the present invention can adopt other embodiments. For example, in the above embodiment, a wall flow type DPF is employed as the PM trapping device, but various other filter structures can be employed. In addition to the honeycomb shape as described above, the shape and structure of the substrate can also be a plate shape, a cylindrical shape, a pellet shape, a mesh shape (for example, a woven or non-woven fabric of inorganic fibers, a metal net), etc. is there.

  Further, the present invention can be applied to all internal combustion engines that may generate PM, in addition to a diesel engine as a compression ignition type internal combustion engine. For example, a direct injection spark ignition internal combustion engine, more specifically, a direct injection lean burn gasoline engine. In this engine, fuel is directly injected into the in-cylinder combustion chamber. However, in a high load region where the fuel injection amount is large, the fuel does not completely burn and PM may be generated. Even if the present invention is applied to such an engine, the same effect as described above can be sufficiently expected.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(1) Experimental apparatus In FIG. 3, the schematic diagram of the experimental apparatus used by the Example and the comparative example is shown. In the experimental apparatus 60 shown in FIG. 3, a simulation gas (MG), which will be described later, passes through the NO oxidation catalyst 62 disposed in the upstream side quartz tube 61, and then the DPF 64 disposed in the downstream side quartz tube 63 is used. It passes through and is discharged outside through an exhaust duct (not shown). Then, oxygen and ozone (or only oxygen) supplied from an ozone generator (not shown) are supplied as an injection gas from a three-way elbow 65 disposed between the upstream side quartz tube 61 and the downstream side quartz tube 63, and simulated. After being mixed with the gas, it is supplied to the DPF 64 together with the simulated gas. Electric heaters 66 and 67 are provided on the outer peripheral portions of the upstream side quartz tube 61 and the downstream side quartz tube 63, respectively, so that the temperatures of the NO oxidation catalyst 62 and the DPF 64 are controlled. Furthermore, temperature sensors 68 and 69 are provided for measuring temperatures at the positions immediately upstream of the NO oxidation catalyst 62 and the DPF 64, respectively.

(2) Experimental conditions The electric heaters 66 and 67 were controlled so that the temperature detected by the temperature sensors 68 and 69 was 200 ° C. The composition of the simulated gas was volume concentration, NO was 210 ppm, O ₂ was 5%, H ₂ O was 3%, the balance was N _2, and the flow rate of the simulated gas was 9.5 L / min. Furthermore, the composition of the injected gas is that ozone is supplied with the ozone generator turned on and the ozone (O ₃ ) is 10,000 ppm and the remainder is O ₂ , while the ozone generator is turned off and the ozone is supplied. When not performed, only O ₂ was used, and the flow rate of the injection gas was 0.5 L / min.

(3) Experimental method N ₂ is allowed to flow until the temperature detected by the temperature sensors 68 and 69 becomes constant (200 ° C.). After that temperature becomes constant, the simulated gas containing NO is allowed to flow. At the same time, O ₂ was introduced into the ozone generator. When ozone was generated, the ozone generator was turned on simultaneously with the introduction of O ₂ .

Note that the oxidation amount (oxidation rate) of PM in the DPF 64 was calculated from the CO and CO ₂ concentrations detected by an exhaust gas analyzer (not shown). That is, by dividing the product of the simulated gas flow rate, the detected volume concentration, and the measurement time by the volume of 1 mol (for example, 22.4 L), the number of mols in the measurement time can be obtained. Based on this, the oxidation amount (oxidation rate) of PM is calculated.

(4) Examples and Comparative Examples (Example 1)
The NO oxidation catalyst 62 and the DPF 64 having the specifications shown below were arranged, and the oxidation amount (oxidation rate) of PM was measured in a state where the power source of the ozone generator was turned on.

<NO oxidation catalyst>
A cordierite honeycomb structure coated with ZrO ₂ having a diameter of 30 mm, a length of 50 mm, a cell wall thickness of 4 mil (milli inch length, 1/1000 inch), and a cell count of 400 cpsi (cells per square inch) was used. The coating amount of ZrO ₂ was 120 g / L. The denominator L (liter) means per 1 L of catalyst (the same applies hereinafter). This was supported with Pt using an aqueous solution containing dinitrodiammine platinum, dried, and calcined at 300 ° C. for 1 hour to obtain a NO oxidation catalyst. The amount of Pt supported was 10 g / L. The NO oxidation catalyst 62 obtained in this way was placed in the upstream side quartz tube 61 for experiments.

<DPF>
A cordierite DPF (catalyst is not coated) having a diameter of 30 mm, a length of 50 mm, a cell wall thickness of 12 mil, and a cell number of 300 cpsi was used. For PM accumulation, a container capable of installing 12 cordierite honeycomb structures with a diameter of 30 mm and a length of 50 mm in parallel is arranged in the exhaust pipe of a diesel engine (displacement 2 L), and operation at 2000 rpm and 30 Nm is arranged here. PM was collected by flowing an exhaust gas under conditions for 1 hour. The DPF 64 on which PM was deposited in this way was placed in the downstream side quartz tube 63 with the surface on which the PM was deposited positioned upstream, and experiments were conducted.

(Comparative Example 1)
The NO oxidation catalyst 62 is not disposed in the upstream side quartz tube 61, and only the DPF 64 on which PM similar to the DPF used in Example 1 is deposited is disposed in the downstream side quartz tube 63, and the simulated gas contains NO. Except that the flow was not performed, the oxidation amount (oxidation rate) of PM was measured in the same manner as in Example 1 (the power supply of the ozone generator was turned on).

(Comparative Example 2)
Example except that the NO oxidation catalyst 62 is not arranged in the upstream side quartz tube 61 and only the DPF 64 on which PM similar to the DPF used in Example 1 is deposited is arranged in the downstream side quartz tube 63. In the same manner as in No. 1 (simulated gas contains NO, the power supply of the ozone generator is turned on), the oxidation amount (oxidation rate) of PM was measured.

(Comparative Example 3)
The amount of PM oxidation (oxidation rate) is measured in the same manner as in Example 1 (NO oxidation catalyst is used, the simulation gas contains NO) except that the ozone generator is turned off and ozone is not supplied. did.

(5) Experimental results In Example 1 and Comparative Examples 1 to 3, the PM oxidation rate 10 minutes after switching from N ₂ to the simulated gas (after introducing O ₂ into the ozone generator) is shown in FIG. . In the figure, the unit g / h / L of the PM oxidation rate on the vertical axis represents the number of grams of PM oxidized per liter of DPF and per hour.

First, from the comparison between the result of Comparative Example 1 and the result of Comparative Example 2, it was confirmed that when NO is present, the PM oxidation rate by ozone is greatly reduced. On the other hand, if 85% of NO is oxidized to NO ₂ by the NO oxidation catalyst in Example 1, the reaction between ozone and NO _x is found from the comparison between the result of Example 1 and the result of Comparative Example 2. It was confirmed that the decrease in the PM oxidation rate due to ozone was sufficiently suppressed. Further, from the comparison between the result of Example 1 and the result of Comparative Example 3, it was confirmed that the PM oxidation rate was significantly reduced when ozone was not supplied.

As described above, according to the present invention, ozone is used in an apparatus for purifying exhaust gas discharged from an internal combustion engine such as a diesel engine using a particulate matter collecting apparatus that collects PM in exhaust gas. An exhaust gas purifying apparatus that can efficiently use ozone when oxidizing and removing PM, and can sufficiently suppress a decrease in the oxidation rate of PM due to NO _x or the like to achieve a high level of PM purification efficiency. It becomes possible to provide.

1 is a schematic view of a preferred embodiment of an exhaust gas purification apparatus of the present invention connected to an internal combustion engine. Is a graph showing the relationship between the ratio and the temperature of the ozone decreases react with NO or NO _2. It is a schematic diagram of the experimental apparatus (exhaust gas purification apparatus) used in the examples and comparative examples. It is a graph which shows the comparison of PM oxidation rate in Example 1 and Comparative Examples 1-3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 15 ... Exhaust gas passage, 20 ... NO oxidation catalyst, 30 ... DPF, 40 ... Ozone supply means, 41 ... Ozone generator, 42 ... Ozone supply passage, 43 ... Ozone supply nozzle, 44 ... Ozone supply port, 50 ... temperature sensor, 100 ... ECU.

Claims (3)

An exhaust gas passage connected to the internal combustion engine;
A particulate matter collecting device disposed in the exhaust gas passage for collecting particulate matter in the exhaust gas;
An ozone supply means connected to the exhaust gas passage upstream of the particulate matter collection device and capable of supplying ozone to the particulate matter collection device;
A NO oxidation catalyst which is disposed in the exhaust gas passage upstream of the ozone supply means and oxidizes NO in the exhaust gas;
An exhaust gas purification apparatus comprising: Exhaust gas temperature detection means for measuring or estimating the temperature of the exhaust gas passing through the particulate matter collection device;
Ozone supply control means for controlling the ozone supply means based on the exhaust gas temperature detected by the exhaust gas temperature detection means;
The exhaust gas purification apparatus according to claim 1, further comprising:   The ozone supply control means is configured to supply ozone when the exhaust gas temperature is within a range of a first predetermined temperature of 50 ° C. or higher and a second predetermined temperature of 300 ° C. or lower. It controls, The exhaust gas purification apparatus of Claim 2 characterized by the above-mentioned.

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